1. Field of the Invention
This invention relates to a nonvolatile semiconductor memory device with a plurality of insulating films and a plurality of electrode films alternately stacked therein.
2. Background Art
In recent years, the integration density of nonvolatile semiconductor memory devices has been rapidly increasing. For instance, JP-A 2007-266143 (Kokai) proposes a three-dimensionally structured nonvolatile semiconductor memory device in which memory cells are vertically stacked on one silicon substrate. In this technique disclosed in JP-A 2007-266143 (Kokai), electrode films and insulating films are alternately stacked on a silicon substrate to form a multilayer body, and then through holes are simultaneously formed in this multilayer body. A charge storage film is formed on the side surface of the through hole, and a silicon pillar is buried inside the through hole. Thus, a memory cell is formed at an intersection between each of the electrode films and the silicon pillar.
In this three-dimensionally structured nonvolatile semiconductor memory device, information can be stored by controlling the potential of each electrode film and each silicon pillar to transfer charge between the silicon pillar and the charge storage film. In this technique, a plurality of electrode films are stacked on the silicon substrate to reduce the chip area per bit, and it allows cost reduction. Furthermore, because the multilayer body is simultaneously processed, increase in the number of stacked films does not result in increasing the number of lithography steps, and cost increase can be suppressed.
However, even in such a three-dimensionally structured nonvolatile semiconductor memory device, still higher integration density is desired.